Various polyester compositions and aqueous dispersions thereof are generally known in the art. Aqueous polyester compositions used in the present invention are normally limited to a solids content of no more than about 30%. In certain applications, it would be desirable to increase the solids content to relatively high levels, say 65%.
Polyester blends are known and are generally prepared by melt blending. However, intimate blends such as provided by the present invention are generally difficult to prepare because of the high melt viscosities of the polyesters involved and the incompatibility of most polyesters with other polymers. Additionally, intimate blends are very difficult to disperse in water if either of the polymers is not water dispersible or water soluble.
Blends can also be prepared in solution followed by removal of solvent, but this approach also has inherent problems. For example, a mutual solvent or solvent mixture must be found that maintains compatibility as the polymer concentration increases during solvent removal.
The formation of one polymer in the presence of another polymer is also a known concept. For example, "core/shell" polymer systems are known in which a crosslinked "core" is first polymerized by emulsion polymerization, followed by addition of a second monomer which is polymerized to form a "shell."
Another example in which an addition polymer is formed in the presence of another polymer is the use of nonionic water-soluble polymers including poly(vinyl alcohol), hydroxyethylcellulose, gum acacia, polyacrylic acid, and various other water-soluble polymers as protective colloids for polymerization of various monomers.
The use of poly(vinyl alcohol) for vinyl acetate polymers and copolymers has been particularly important commercially as illustrated in U.S. Pat. No. 3,708,388.
U.S. Pat. No. 4,335,220 describes the use of water-dispersible polyesters as sequestering agents for water-immiscible solids and liquids. The material to be dispersed must be a hydrophobic deformable organic substance.
U.S. Pat. No. 4,119,680 (Vachon) describes grafted water-dispersible copolyesters useful as binders and finishes for polyester-containing fabrics. The polyesters contain .alpha.,.beta.-unsaturated dicarboxylic acids to provide sites for grafting. The graft copolymers are prepared by polymerization of vinyl or acrylic monomers in aqueous dispersions of these polyesters.
Water-soluble unsaturated polyester salts have been used to emulsify styrene to make polymers (Y. Ch. Chu and W. Funke, Angew. Makromol. Chem., 1982, No. 103, p. 187, 203; W. Funke et al., Makromol. Chem., 180, 1979, p. 2797; M. Narkis, J. Appl. Polym. Sci., 23, 1979, p. 2043; H. Baumann, B. Joos and W. Funke, Macromol. Chem. Phys., 1986, Vol. 187, p. 2933). The work directed by Funke concerns polyesters which are carboxyl terminated. The emulsifying properties are only observed if the carboxyl groups are completely dissociated, which requires a weakly alkaline environment (pH ca. 8.5). Work has been done with both saturated and unsaturated polyesters. These are low molecular weight polyesters with number average molecular weights reported from 1,000 to 3,000. Funke reports that at very short chain lengths the polyesters do not emulsify at all, and at higher molecular weights the polyesters are water insoluble even when the carboxyl groups are neutralized.
At the August 1987 national ACS meeting a paper was presented by F. Cuirassier, Ch. H. Baradji and G. Riess on the preparation of microlatices in the presence of functionalized polyesters. The polyesters used were carboxy-terminated with number average molecular weights in the range of 1,000 to 4,000. Styrene and acrylic monomers were polymerized to form microemulsions. These polyesters appear to be similar to those used by Funke and therefore have similar limitations.
There exists a need for polyvinyl acetate latices that provide better adhesion properties for various coatings such as faster bonding, better hold-out, i.e.. not easily absorbed into the substrate, etc.
One object of the present invention is to provide latices of polyvinyl acetate and copolymers thereof, useful as adhesives, in paper coatings and in inks that exhibit:
a. faster setting or bonding speeds. PA1 b. high solids level (up to 65%). PA1 c. improved "hold out"; and PA1 d. high gloss. PA1 (a) at least one dicarboxylic acid, PA1 (b) from about 4 to about 25 mole percent, based on the total of all acid and hydroxyl monomers being equal to 200 mole percent, of at least one difunctional sulfomonomer containing at least one metal sulfonate group attached to an aromatic nucleus wherein the functional groups are hydroxyl or carboxyl, and PA1 (c) at least one glycol, and about 95-50% by weight of a polymer or copolymer of vinyl acetate having repeat units from about 50 to 100 weight percent vinyl acetate and said polymer or copolymer having been polymerized in an aqueous dispersion of said polyester. PA1 (1) about 5% to about 35% of a polyester having an I.V. of at least 0.1 and having repeat units from PA1 and PA1 (2) at least one vinyl monomer of which about 50 to 100 weight percent is vinyl acetate, PA1 and
Another object is to provide latices of polyvinyl acetate and copolymers thereof that are free of surfactants or wetting agents.
The present invention further provides substrates adhered together by the dried residue of the aqueous dispersion of the present invention.